In general, two processes are used for colouring keratin-containing fibres. A first method relates to the well known oxidation dyes which are formed by oxidative coupling of one or more developer components (primary intermediates) with one or more coupler components. When using oxidizing agents, however, damage to the hair structure is observed. Furthermore, some of the oxidation hair colour precursors used may have a sensitization potential. If required, oxidation-stable direct dyes can also be added to the oxidative system in order to achieve particular colour effects. Another possibility consists in the exclusive use of direct dyes. These direct dyes are used in a suitable carrier masses. This method, generally known as tinting, is easy to use, exceptionally mild and is characterized by low damage to the keratin fibres since no ammonia or peroxide is added. These dyes should meet at least some basic requirements such as durability, washing and light fastness, good toxicological and dermatological profiles and, if desired, stability towards oxidizing agents (e.g. hydrogen peroxide). A colouration system based on direct dyes often requires combinations of several dyes to obtain the desired variety of different shades. This fact is of particular interest in the case for dark colours like black shades. Normally, black shades can only be achieved by a mixture of several different direct dyes with different dyeing properties (e.g. diffusion etc.). It therefore would be desirable to have only one single black direct dye instead of a mixture of diverse direct dyes.
Griffith and Riepl (Griffith/Riepl, Chem. Commun 1998, pp 1349-1350) published a route towards black-bluish monoazo disperse dyes and their use in liquid crystal displays and optical filters. The publication in Dyes and Pigments, Vol. 27, No. 1, pp 45-54 (1995) and Dyes and Pigments, Vol. 37, No. 4, pp 283-289 (1998) disclose special 4-amino-2-arylazothiazoles which shall have a good stability and shall be superior in some cases both thermally and photochemically, relative to standard azo dyes; hair dyes are not disclosed. WO 2005/117816 A1 discloses cationic quinoxaline thiazole azo dyes and their use in colorants for keratin fibers. DE 102004056403 A1 discloses cationic pyridinylthiazo dyes and their use in colorants for keratin fibers. DE 102004051072 A1 discloses cationic heteroarylpyrazolonazo dyes and their use in colorants for keratin fibers.